An immunoradiometric assay (IRMA) has been developed and field tested in conjunction with scientists at NYU which can detect and identify malaria sporozoites in wild-caught mosquitoes. The test uses species-specific hybridoma- produced monoclonal antibodies and can quantify sporozoite levels resulting from a single oocyst. The IRMA should prove to be an important tool for studies of malaria epidemiology. Circumsporozoite (CS) proteins have been shown to be the protective antigens of several species of malaria. The CS polypeptides of the various malaria species can be differentiated using monoclonal antibodies although these species specific polypeptides are structurally related and belong to a family of homologous proteins. A cDNA clone that expresses the CS antigen of Plasmodium knowlesi in E. coli has been developed.